As this type of battery power supply system there is a conventionally known arrangement that includes a box having a cooling air inlet on one end face and a suction fan within a section at the other end, and a battery assembly housed within the box. The battery assembly is formed from a plurality of battery module groups that are arranged at intervals in parallel to each other along a cooling air flow direction; each battery module group is formed from a plurality of rod-shaped battery modules that are arranged, within an imaginary plane intersecting the cooling air flow direction, at equal intervals with their axes intersecting the cooling air flow direction, and the axes of one rod-shaped battery module and another rod-shaped battery module that is adjacent thereto in the cooling air flow direction are positioned within an imaginary plane that is parallel to the cooling air flow direction.
In this case, with regard to each battery module group, the module group that is closest to the cooling air inlet is cooled best, but the extent of cooling of the battery module groups decreases the further away they are from the cooling air inlet, while also depending on the positional arrangement, and the overall temperature variation across the battery module groups is large.
In order to improve the durability of the battery module groups by cooling them uniformly, certain cooling measures have been taken. For example, one measure that has been taken is to place synthetic resin rectifying plates in spaces surrounded by four battery module groups, thus appropriately controlling the flow rate of the cooling air in the vicinity of the battery modules and thereby suppressing the temperature variation (e.g., Japanese Patent Application Laid-open No. 10-255859).
However, this conventional arrangement has the problems that, since a rectifying plate manufactured with high dimensional precision is required, the cost of a mold therefore is high, and in the initial stages of cooling the rectifying plate must be cooled at the same time, which is wasteful; furthermore, since the cooling air passage is narrowed by the rectifying plate, dirt and dust easily collect in the passage and there is also a possibility that a short circuit might be caused when condensation, etc. occurs and, moreover, since the cooling air passage is a long, narrow passage, the overall pressure loss across the box is high, and a high output suction fan is required.